Scientists say they have made a blocker that could stop the lethal anthrax toxin from attacking the body.

The inhibitor binds to the receptors in the body where anthrax attaches.

Using receptors as the treatment target rather than the toxin itself should get round the problem of antibiotic resistance, the PNAS journal reports.

The same approach could also be used to stop other deadly invaders such as SARS, influenza and Aids, the US and Canadian researchers said.

Inhibition

The current treatment for anthrax exposure is antibiotics.

But pathogens can mutate and develop resistance to these treatments, rendering them ineffective.

With anthrax, there is also a concern that individuals could intentionally alter the toxin in the lab to make it resistant to current treatments, producing an even more deadly bioterrorism agent than it already is.

The inhibitor represents a step forwards in treatment but does not obviate the need for development of better and more effective vaccines to prevent anthrax

Dr Shiranee Sriskandan, consultant in infectious diseases at Imperial College London

Inhalation of anthrax still has a fatality rate of 75%, even after antibiotics are given.

Antibiotics can slow the progression of the infection, but they do not counter the advanced destructive effects of the anthrax toxin in the body.

Dr Ravi Kane, from the Rensselaer Polytechnic Institute in New York, and his colleagues believe that combining their inhibitor with antibiotic therapy may increase the chance of survival for people who become infected with anthrax by neutralising the toxin.

Best fit

They tested the inhibitor in rats to find the best design.

This was a polyvalent inhibitor, which means that it displays multiple copies of receptor-binding peptides, allowing it to bind at multiple sites and become more potent than inhibitors that bind to a single site.

All of the six animals they injected with the polyvalent inhibitor appeared to be protected from anthrax, with no signs of adverse side effects.

Work is now needed to see whether the inhibitor will do the same in humans.

Dr Shiranee Sriskandan, a consultant in infectious diseases at Imperial College London, UK, said: "There have been many other approaches to blocking the anthrax toxin; what is important about this work is that the investigators have come up with a new technique for screening chemicals for activity that might block other types of toxin as well.

"It will be important in future work to establish whether such an approach can work in 'real' infections.

"The inhibitor represents a step forwards in treatment but does not obviate the need for development of better and more effective vaccines to prevent anthrax, which remains an important disease in many poor, developing countries, notwithstanding the risks of misuse in bioterrorism."

Researchers at Oxford University are among others searching for an effective anthrax inhibitor.